Luminescence properties and temperature sensing characteristics of Bi2WO6: Er3+, Tm3+, Yb3+ phosphors

Bi2WO6:x%Er3+, y%Tm3+, 6%Yb3+ (x = 0, 0.5, 1, 2, 4, 6; y = 0, 1) upconversion luminescent materials were prepared via a high-temperature solid-state method. XRD studies showed that Er3+, Tm3+ and Yb3+ doping at various concentrations had little effect on the orthorhombic structure of the Bi2WO6 crystal system. SEM images showed that the morphologies of the Bi2WO6: 1%Tm3+, 6%Yb3+ and Bi2WO6: 4%Er3+, 1%Tm3+, 6%Yb3+ powder samples were uneven, with agglomeration of nearly spherical particles and particle sizes of 0.5–5 μm. The average granularities of the samples were slightly smaller after Er3+ codoping. With 980 nm excitation (power: 500 mW), Bi2WO6: 4%Er3+, 6%Tm3+, 6%Yb3+samples exhibited the strongest luminescence upconversion. With increasing Er3+ doping levels, the intensity of Er3+ luminescence in the Bi2WO6: x%Er3+, 1%Tm3+, 6%Yb3+ samples first increased and then decreased, whereas the Tm3+ luminescence significantly decreased, indicating energy transfer from Tm3+ to Er3+. For Bi2WO6: 4%Er3+, 1%Tm3+, 6%Yb3+ samples excited with 100–500 mW powers and at 980 nm, the 525 nm and 530 nm green emission peaks for Er3+ and 685 nm and 705 nm red emission peaks for Tm3+ resulted from two-photon absorption. For the Bi2WO6: 4%Er3+, 1%Tm3+, 6%Yb3+ sample excited at 980 nm, the temperature was characterized by the I543nm/I705nm fluorescence intensity ratio; at 298 K, the maximum Sa was 0.806 K-1, and the maximum Sr was 0.0243 K-1. When the temperature was characterized by the I705nm/I525nm fluorescence intensity ratio, Sa was 0.0256 K−1 at 573 K, and the maximum Sr was 0.0382 K-1. At 298 K, the sample showed a minimum temperature resolution of 0.026 K. As the temperature increased from 298 K to 573 K, the luminescence color of the sample gradually shifted from the green to orange-yellow.